1. Field of the Invention
This invention relates to a document converting display system by which a low resolution display signal from a personal computer is displayed on a display apparatus of high resolution used in a CAD (computer-aided design)/CAM (computer-aided manufacturing) apparatus or the like.
2. Description of the Prior Art
Most personal computers use a display apparatus which has a display resolution of about 640.times.200 to 640 .times.350 dots. An image display work station used in a CAD/CAM system or the like, however, employs a display apparatus which has a high display resolution of 1024.times.1024 dots.
It is frequently desirable that the data accumulated by use of the application programs used in a personal computer be utilized by a work station. To this end, there is proposed a method in which data sets are produced by the personal computer and written in the data area of the work station side. This method, however, needs a function for transferring the data sets from the application program used in the personal computer. Also, it is necessary to provide a function for receiving the data sets in the application program of the work station side. There is, of course, the simple method in which the display for the personal computer is provided adjacent to the work station and data is displayed on the display at any time. This requires the display of the personal computer and the display of the work station to be placed side-by-side on the desk. Thus, the whole system becomes large-scaled. When both displays are used at the same time, the user has to see two display apparatus to check the respective work contents, so that the work efficiency will be lowered.
Therefore, it is necessary for the display apparatus of high resolution for, for example, the work station to be able to display data derived from a personal computer.
To this end, the following methods are proposed in the art:
A. A display which can select a plurality of horizontal scanning frequencies is used and the mode of a display controller is changed. PA1 B. The display routine of a display for an application program is rewritten. PA1 C. Access to the display controller for the personal computer is analyzed from a hardware standpoint and a program in which it is converted into a form suitable for the display controller of the work station is executed by a host processor. PA1 D. A V-RAM (video-random access memory) of the display controller for the personal computer and a V-RAM of the display controller for the work station are shared by a single V-RAM. PA1 (a) storing the low resolution video display signals in a first memory; PA1 (b) reading out the video display data contents of the first memory and storing them in a buffer memory at a rate which is a function of the first synchronizing signals; PA1 (c) storing the high resolution video display signals in a second memory; PA1 (d) selectively reading out the contents of the buffer memory and a selected portion of the second memory, at a rate which is a function of the second synchronizing signals, and simultaneously displaying the read out video data on a display with the contents of the buffer memory being displayed in window fashion amid the contents of a portion of the second memory.
These methods, however, have the following defects:
According to the method A, the display itself becomes expensive and a display of high resolution can not be expected.
According to the method B, it is substantially impossible for the user to rewrite the application program. According to the method C, the host processor must execute the program to be analyzed and the work station must be constructed as a multi-task or multi-processor in order to execute the application program at the same time.
According to the method D, the rate in which the V-RAM is used becomes high due to the double access of the V-RAM and hence the operation speed of the V-RAM must be increased. Since the data to be displayed is not limited to the data of a dot image but includes formats having a proper meaning such as attribute or the like, it becomes necessary to provide hardware for analyzing these data.
According to the prior art, as described above, a display apparatus of high resolution could not easily display a display signal derived from a personal computer of low resolution.